Update monitor event id on duplicate inbound claim

The first time we claim an HTLC in a channel, we may not have an associated
monitor event id. Once we later process the monitor event for the claim, we
need to update the channel's internal htlc state to include the monitor event
id, so the event can be properly acked afer the htlc is removed.

Author: valentinewallace

lightning/src/ln/channel.rs

@@ -7535,7 +7535,8 @@ where
 
 		let mut pending_idx = core::usize::MAX;
 		let mut htlc_value_msat = 0;
-		for (idx, htlc) in self.context.pending_inbound_htlcs.iter().enumerate() {
+		let channel_id = self.context.channel_id();
+		for (idx, htlc) in self.context.pending_inbound_htlcs.iter_mut().enumerate() {
 			if htlc.htlc_id == htlc_id_arg {
 				let expected_hash =
 					PaymentHash(Sha256::hash(&payment_preimage_arg.0[..]).to_byte_array());
@@ -7549,10 +7550,17 @@ where
 				);
 				match htlc.state {
 					InboundHTLCState::Committed { .. } => {},
-					InboundHTLCState::LocalRemoved { ref reason, .. } => {
+					InboundHTLCState::LocalRemoved {
+						ref reason,
+						monitor_event_id: ref mut id,
+						..
+					} => {
+						if monitor_event_id.is_some() {
+							*id = monitor_event_id;
+						}
 						if let &InboundHTLCRemovalReason::Fulfill { .. } = reason {
 						} else {
-							log_warn!(logger, "Have preimage and want to fulfill HTLC with payment hash {} we already failed against channel {}", &htlc.payment_hash, &self.context.channel_id());
+							log_warn!(logger, "Have preimage and want to fulfill HTLC with payment hash {} we already failed against channel {channel_id}", &htlc.payment_hash);
 							debug_assert!(
 								false,
 								"Tried to fulfill an HTLC that was already failed"
@@ -7593,17 +7601,24 @@ where
 			// `claim_htlc_while_disconnected_dropping_mon_update` and must match exactly -
 			// `claim_htlc_while_disconnected_dropping_mon_update` would not work correctly if we
 			// do not not get into this branch.
-			for pending_update in self.context.holding_cell_htlc_updates.iter() {
+			for pending_update in self.context.holding_cell_htlc_updates.iter_mut() {
 				match pending_update {
-					&HTLCUpdateAwaitingACK::ClaimHTLC { htlc_id, .. } => {
+					&mut HTLCUpdateAwaitingACK::ClaimHTLC {
+						htlc_id,
+						monitor_event_id: ref mut id,
+						..
+					} => {
 						if htlc_id_arg == htlc_id {
 							// Make sure we don't leave latest_monitor_update_id incremented here:
 							self.context.latest_monitor_update_id -= 1;
+							if monitor_event_id.is_some() {
+								*id = monitor_event_id;
+							}
 							return UpdateFulfillFetch::DuplicateClaim {};
 						}
 					},
-					&HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. }
-					| &HTLCUpdateAwaitingACK::FailMalformedHTLC { htlc_id, .. } => {
+					&mut HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. }
+					| &mut HTLCUpdateAwaitingACK::FailMalformedHTLC { htlc_id, .. } => {
 						if htlc_id_arg == htlc_id {
 							log_warn!(logger, "Have preimage and want to fulfill HTLC with pending failure against channel {}", &self.context.channel_id());
 							// TODO: We may actually be able to switch to a fulfill here, though its